The invention relates to a switched-mode power supply device which can be used notably in an aircraft, for example an airplane, and an aircraft including at least one such device.
The technical field of the invention is that of switched-mode power supply devices and that of the protection of the electrical devices which they power against network power brown-outs or the presence of a supply voltage below a threshold. Below this threshold the switched-mode power supply device no longer operates satisfactorily. In the remainder of the description, the term brown-out will be used, but this also encompasses a network supply voltage below the threshold.
A switched-mode power supply device is considered, which receives at its input a direct current voltage deriving from a direct current voltage network or, by extension, resulting from the rectification of an alternating current voltage deriving from an alternating current network, where the network is subject to a risk of brown-out. The goal of the invention is to enable this power supply device to continue to operate satisfactorily, i.e. to continue to supply its output voltages, during a network brown-out, when it is deprived of its energy source for a short time, or when it is powered by a voltage which is too low. In the case of a longer disconnection, the power source eventually ceases to operate, but with a certain delay, which can enable a powered device to stop under optimum conditions.
Most known solutions consist in incorporating an electrical power reserve, generally a capacitor, in the power supply device. This power reserve is charged and kept charged when a network voltage is present, in normal operation. It is used as an energy source, and is discharged to allow the power supply device to operate during a brown-out, when the network no longer supplies energy, either because it can no longer supply current, or because its voltage has fallen too low to be able to be used by the power supply device.
The invention concerns cases in which this power reserve is charged by a dedicated DC-DC converter called a charger, providing certainty that the quantity of stored energy does not depend on the value of the network voltage. The power supply device includes, in general in addition to the charger and the power reserve, DC-DC converters called output converters, the role of which is to deliver direct output voltages, where these output voltages are regulated and take on desired values: for example: +5 V; +3.3 V; +/−15 V, where these values are common in the field of aeronautics.
Depending on the way in which the charger and the power reserve are connected, the structure of the power reserve may be a “series” or “parallel” structure.
In a series structure, illustrated in FIG. 1, the charger 10 is connected by one input to a direct current power supply network RC. It is traversed by the full input power supplied by the network RC. It is connected by one output to a power reserve 11. Several output DC-DC converters 12 are connected by one input to the terminals of the power reserve 11. In the remainder of the description the term “several” means at least two. Output converters 12 supply at their output regulated output voltages VS.
After having traversed the charger 10, this input power is used, firstly, to charge the power reserve 11 and, secondly, by the output converters 12.
Such a series structure has the following advantages:
The inputs of the output converters 12 are subject to a direct current voltage which is regulated during normal operation, independently of the fluctuations of the network.
The output converters 12 are permanently connected to the power reserve 11. They are therefore not disrupted at the start of the brown-out, when they cease to use the energy of the network RC, and start using that of the power reserve 11. The same applies at the end of the brown-out.
Conversely:
The charger 10 permanently causes losses, including during normal operation.
To use the energy stored in the power reserve 11 satisfactorily, the output converters 12 must be able to operate with a voltage at their input which is much lower than that which is present during normal operation.
In a parallel structure, illustrated in FIG. 2, the charger 10 is shunt connected with the network RC. The power reserve 11 is connected to an output of the charger 10. The charger 10 takes only the power required to charge the power reserve 11. A switch 15 with two inputs and one output is present. Its output is connected to an input of the output converters 12. One of its inputs is connected to a node which is common to the output of the charger 10 and the power reserve 11. Its other input is connected to the network RC.
In a first position, the switch 15 connects the input of the output converters 12 to the power reserve 11; in a second position it connects the input of the output converters 12 to the network RC.
The output converters 12 are powered, in normal operation, by the network RC, i.e. upstream from the charger 10. The switch 15 is in the second position.
In the presence of a brown-out, the output converters 12 are powered by the power reserve 11. The switch 15 is in the first position.
It is preferable to install a parallel bypass capacitor 19 connected at the input of the output converters 12; it enables a sufficient voltage to be maintained at the input of the output converters 12 during operation of the switch 15.
Such a parallel structure has the following advantage. The charger 10 generates significant losses only during the period of initial charging of the power reserve 11.
Conversely, at the start of a brown-out, when the energy originating from the network RC ceases to be used, and instead that of the power reserve 11 is used, the output converters 12 must be disconnected from the network RC, and connected to the power reserve 11 using the switch 15. The same applies at the end of the brown-out. This leads to difficulties with, notably, the following risks: interrupted operation of the output converters 12, current peaks at the time of the connection between portions of circuits including capacitors charged at different voltages, oscillations, discharge of the power reserve 11 to the network RC, untimely oscillations of a decision-making logic intended to control the switch 15.
To use the energy stored in the power reserve 11 satisfactorily, the output converters 12 must be capable of operating across a wide input voltage range.
The output converters 12 experience at their inputs the variations of the network voltage RC in normal operation.